Method of treating diabetic angiopathy

ABSTRACT

This invention relates to a method of treating patients afflicted with diabetic angiopathy. The method includes administering to a patient in need of treatment an effective amount of a thiol or reducible disulfide compound according to the formula set forth in the specification.

FIELD OF THE INVENTION

This invention relates to a method for treating a patient suffering fromdiabetic angiopathy. The method involves administering an effectiveamount of a disulfide or thiol-containing compound to a patientsuffering from an ischemic condition.

BACKGROUND OF THE INVENTION

One of the many common complications of diabetes is angiopathy, orabnormality of the blood vessels. Angiopathy of this sort is thought tobe mediated by the action of the enzyme aldose reductase. The conditiongenerally results in abnormalities categorized by reduced blood flow,weakening of vessel walls with the tendency to develop aneurysms,restenosis, atherosclerosis, and other conditions. Diabetic angiopathyresults in a chronic degradation of vessel structure, to the point wherethe condition becomes severely life-threatening.

Current methods do little to reduce or obviate the onset of diabeticangiopathy. The current popular treatment involves the administration ofangiotensin converting enzyme (ACE) inhibitors such as captopril, topatients with chronic angiopathy as a result of diabetes. Calciumchannel blockers have also been administered for this purpose, and ahigh protein diet has also been suggested to slow the onset ofangiopathy. It has been suggested that the only true way to preventdiabetic angiopathy (and other diabetic complications) is through strictglycemic control.

Aldose reductase (AR) inhibitors have been tested in humans, mainly inthe 1980s, with the hope that these agents would slow the progress ofdiabetic retinopathy, a condition that often led to blindness. The ARinhibitors (sorbinil was one of those tested) showed some efficacy, butwere not well tolerated by patients. No AR inhibitor to date has beenapproved for use in the United States for diabetic angiopathy or anyother indication.

Mesna (sodium 2-mercaptoethene sulfonate) and dimesna (disodium2,2′-dithiobis ethane sulfonate) are known therapeutic compounds, whichhave heretofore demonstrated a wide variety of therapeutic uses. Bothmesna and dimesna have been shown to be effective protective agentsagainst certain specific types of toxicity associated with theadministration of cytotoxic drugs used to treat patients for varioustypes of cancer. In particular, mesna has been used with some success inmitigating the toxic effects of cytotoxic agents such as ifosfamide,oxazaphosphorine, melphalane, cyclophosphamide, trofosfamide,sulfosfamide, chlorambucil, busulfan, triethylene thiophosphamide,triaziquone, and others, as disclosed in U.S. Pat. No. 4,220,660, issuedSep. 2, 1980.

The near absence of toxicity of dimesna further underscores theusefulness of this compound, as large doses that can be given to apatient without increasing the risk of adverse effects from theprotective agent itself.

Further, pharmacological profiles of each compound indicate that, ifproper conditions are maintained, mesna and dimesna do not prematurelyinactivate primary therapeutic drugs to a significant degree. Thus,neither compound will significantly reduce activity of thechemotherapeutic agent, and in many cases, act to potentiate the effectof the main drug on targeted cancer cells.

The structures of both mesna and dimesna are shown below as Formula aand Formula b respectively.

SH—CH₂—CH₂—SO₃Na  (a)

NaO₃S—CH₂—CH₂—S—S—CH₂—CH₂—SO₃Na  (b)

As is well known, dimesna is a dimer of mesna, with the optimumconditions for oxidation occurring in the slightly basic (pH ˜7.3),oxygen rich environment found in blood plasma. In mildly acidic, lowoxygen conditions, in the presence of a reducing agent such asglutathione reductase, conditions prevalent in the kidneys,intracellular spaces, intestines, and others, the primary constituent ismesna.

Mesna acts as a protective agent for a number of cytotoxic agents bysubstituting a nontoxic sulfhydryl moiety for a toxic hydroxy (or aquo)moiety. This action is particularly evidenced in the coadministration ofmesna and oxazaphosphorine, and in the administration of dimesna alongwith cisplatin, carboplatin, and taxane derivatives.

Mesna and dimesna, as well as some analogues of these compounds, haveexcellent toxicity profiles in mammalian species. In fact, dimesna hasbeen administered intravenously to mice and dogs in doses higher thanthe accepted oral LD₅₀ for common table salt (3750 mg/kg), with noadverse effects. Dimesna has also been administered to humans in dosesexceeding 15 g/m², with no adverse effects.

Mesna, and other analogues with free thiol moieties, constitute the morephysiologically active form of the two types of compounds described inthis specification. These compounds manifest their activity by providingfree thiol moieties for terminal substitution at locations where aterminal leaving group of appropriate configuration is located.

Dimesna and other disulfides can be activated intracellularly byglutathione reductase, a ubiquitous enzyme, thereby generating highconcentrations of intracellular free thiols. These free thiols act toscavenge the free radicals and other nucleophilic compounds oftenresponsible for causing cell damage.

This profile is especially significant in explaining the success ofdimesna in controlling and mitigating the toxic effects of platinumcomplex antitumor drugs. The mechanism for action in the case ofcisplatin (cis-diammine dichloro platinum) is explained in U.S. Pat. No.5,789,000, which is incorporated herein by reference.

Mesna, dimesna, and analogues of these compounds have been the subjectof several prior pharmaceutical uses described in the literature and inprior patents, both in the United States and around the world. Inaddition to the cytotoxic agent protection uses, one or more of thesecompounds have proven effective, in vitro, against a multiplicity ofbiological targets, and have been effective, in vivo, in the treatmentof sickle cell disease, radiation exposure, chemical agent exposure, andother uses.

Mesna, dimesna, and analogues thereof are synthesized from commonlyavailable starting materials, using acceptable routes well known in theart. One such method involves the two-step, single pot synthetic processfor making dimesna and like compounds of the following formula:

 R₁—S—R₂;

wherein:

R₁ is hydrogen, X-lower alkyl, or X-lower alkyl-R₃;

R₂ is -lower alkyl-R₄;

R₃ and R₄ are each individually SO₃M or PO₃M₂;

X is absent or X is sulfur; and

M is an alkali metal.

The process essentially involves a two step single pot syntheticprocess, which results in the conversion of an alkenyl sulfonate salt oracid to the desired formula I compound. The process in the case of mesnais a single step process, which converts the alkenyl sulfonate salt tomesna or a mesna derivative by reacting with an alkali metal sulfide orwith hydrogen sulfide.

If the desired end product is dimesna or a dimesna analogue, a two-stepsingle pot process is involved. Step 1 is as described above. Step 2 ofthe process is performed in the same reaction vessel as Step 1 withoutthe need to purify or isolate the mesna formed during that step. Step 2includes the introduction of oxygen gas into the vessel, along with anincrease in pressure and temperature above ambient values, at least 20pounds per square inch (psi) and at least 60° C. Dimesna or a derivativethereof is formed in essentially quantitative yield.

Other processes, well known and documented in the prior art, may beemployed to make either mesna or dimesna, or derivatives and analoguesthereof.

SUMMARY OF THE INVENTION

This invention involves the administration of an effective amount ofcompounds of formula I, below, for treating patients prone to developdiabetic angiopathy and for treating those already suffering from thatcondition.

wherein:

R₁ is hydrogen, lower alkyl or

R₂ and R₄ are each individually SO₃ ⁻M⁺, PO₃ ²⁻M₂ ²⁺, or PO₂S²⁻M₂ ²⁺;

R₃ and R₅ are each individually hydrogen, hydroxy or sulfhydryl;

m and n are individually 0, 1, 2, 3 or 4, with the proviso that if m orn is 0, then R₃ is hydrogen; and

M is hydrogen or an alkali metal ion; or

a pharmaceutically acceptable salt thereof.

Effective amounts of the formula I compounds to be administeredaccording to the method of this invention vary, and depend on theseverity of the patient's distress.

Accordingly, it is an object of this invention to provide for a methodof safely and effectively treating and/or preventing the onset ofdiabetic angiopathy.

Another object is to provide a method of treating diabetic angiopathy byadministration of a thiol or reducible disulfide to the patient in needof treatment.

Other objects will become apparent upon a reading of the followingdescription.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments herein described are not intended to beexhaustive nor to limit the invention to the precise form disclosed.They are chosen and described to explain the principles of theinvention, and its application and practical use to best enable othersskilled in the art to follow its teachings.

The method of this invention involves the administration of an effectiveamount of a formula I compound to a patient suffering from diabeticangiopathy. Administration may be either oral or parenteral.

The effective amount of the formula I compound will necessarily dependupon the severity of the patient's condition. Since the formula Icompounds are essentially nontoxic (over 40 g/m² have been intravenouslyadministered in a single dose to human patients with no adverseeffects), large amounts can be safely administered. The preferred dosageto treat diabetic angiopathy may be as low as 0.1 mg/kg up to 1,000mg/kg. The more severe the condition, the greater the amount and/orfrequency of dose of the formula I compound should be administered toprovide an effective response.

The following examples illustrate the efficacy of the formula Icompounds in inhibiting AR.

EXAMPLE 1

Aldose reductase assays were as described in Nishimura C., Yamaoka T.,Mizutani M., Yamashita K., Akera T., Tanimoto T., Purification AndCharacterization Of The Recombinant Human Aldose Reductase Expressed InBaculovirus System, Biochem. Biophys. Acta, Jun. 24, 1991;1078(2):171-8.

Briefly, Dimesna (0-20 μM) was incubated at 37° C. with aldose reductase(0.0016 units, human recombinant, expressed in SF 9 cells) and NADPH(0.15 mM) in sodium phosphate buffer (100 mM, pH 6.2). To initiateassays, glucose (10-150 mM) was added to reactions and the decrease inabsorbance at 340 nm (oxidation of NADPH) was monitored. Assays were runin duplicate or triplicate. Slopes were calculated using Varian-Carysoftware package 2.0 and averaged. In all cases errors were 4% or less.Lineweaver Burk analysis (Enzyme Kinetics, version 1.61) was used tocalculate inhibition constants.

EXAMPLE 2

Aldose reductase assays were as described above. Dimesna (0-30 mM) wasevaluated for its effect on the NADPH dependent reduction ofglyceraldehyde (0.050-6 mM) to aldose at 37° C. Assays were run induplicate or triplicate. Slopes were calculated using Varian-Carysoftware package 2.0 and averaged. In all cases errors were 4% or less.Lineweaver Burk analysis (Enzyme Kinetics, version 1.61) was used tocalculate inhibition constants.

Administration is preferably through parenteral or oral routes. Forparenteral administration, the formula I compound is dissolved in asuitable solvent, most preferably water, to produce a solution that maybe injected or infused. One or more pharmaceutically acceptableexcipients may also be added to provide for an elegant formulation asdefined in the art.

For oral administration the formula I compound is preferably combinedwith one or more pharmaceutically acceptable excipients, fillers and/ordiluents. Oral dosage forms may include pills, caplets, tablets, andothers. Alternatively, the formula I compound may be contained in aswallowable container such as a gelatin capsule or the like.

Administration of the formula I compound should be made as soon aspossible following a test confirming the diagnosis of diabeticangiopathy. Preferred initial dose is between 2 mg/kg and 500 mg/kg.Careful observation and blood analysis is performed regularly afterdiagnosis as per accepted medical procedures for treating diabeticangiopathy.

For prophylactic dosing of patients with diabetes who are judged likelyto develop diabetic angiopathy, daily dosing with the formula I compoundis preferred, with the preferred daily dose being split into severalspaced individual doses. Preferred amounts range from 20 mg/day up to 2g/day.

Other accepted methods of treatment, such as co-administration of ACEinhibitors or recommending a high protein diet, may also be combinedwith the administration of the formula I compound. Due to the excellentsafety profile, additional doses of the formula I compound may beadministered safely if the initial dose does not produce a response.

It is understood that the above description is in no way limiting of theinvention, which may be modified within the scope of the followingclaims.

What is claimed is:
 1. A method of treating a patient afflicted withdiabetic angiopathy, said method comprising administering an effectiveamount of a compound of formula I:

wherein: R₁ is hydrogen, lower alkyl or

R₂ and R₄ are each individually SO₃ ⁻M⁺, PO₃ ²⁻M₂ ²⁺, or PO₂S²⁻M₂ ²⁺; R₃and R₅ are each individually hydrogen, hydroxy or sulfhydryl; m and nare individually 0, 1, 2, 3 or 4, with the proviso that if m or n is 0,then R₃ is hydrogen; and M is hydrogen or an alkali metal ion; or apharmaceutically acceptable salt thereof.
 2. The method of claim 1wherein the effective amount of the formula I compound administered isfrom 0.1 mg/kg of body weight to 2,000 mg/kg of body weight.
 3. Themethod of claim 1 wherein the compound is administered orally.
 4. Themethod of claim 1 wherein the compound is administered parenterally.